This invention describes a method and apparatus for indicating the vertical. More particularly it relates to a pendulous type of vertical indicator.
Vertical indicating devices are needed in various situations, particularly in military fire-control system applications and navigation and guidance applications. Pendulous vertical indicators actually determine the direction of total acceleration--which aligns with the vertical. In the presence of lateral accelerations or shocks due to motion of the vehicle in which the pendulum is mounted, the direction indicated by the pendulum is erroneous because the pendulum actually responds to the vector sum of gravity acceleration -g and the lateral accelerations, and, thus may read accurately only under static conditions.
Pendulums may be classified as either mathematical or compound. The mathematical pendulum is characterized by a mass concentrated at a single point at distance, l, from the pivot axis. This pendulum exists only as an idealized model and its calculated natural period is given by l/2.pi.g. Real-life or compound pendulums, on the other hand, have a mass which is distributed along its body. As is well known to those skilled in the art, the compound pendulum has an equivalent or effective length, l, which is related to the distance, l', of its center-of-mass from the pivot axis, and its moment of inertia I around this axis. This length is given by I/ml'., where m is the total mass of the pendulum.